The present invention relates to an improved adjustable pneumatically operated cylinder for use on exercise equipment or chairs. The cylinder is particularly equipped with an external tube in which a piston and an adjustable piston are disposed head to head so as to form a variable air chamber therebetween. The adjustable piston is connected to an adjustment bolt which can be adjusted relatively with respect to an adjustment base fixed to the bottom of the external tube so as to make the adjustable piston move upward to reduce the size of the air chamber, resulting in the increase of the air pressure therein or downward to increase the size of the air chamber, resulting in the decrease of the air pressure. Thereby, the operation pressure of the cylinder can be properly adjusted according to practical requirements.
Pneumatic or air-operated cylinders have been widely used to serve as a damper in a wide range of applications, such as the liftable back doors of a van, exercise equipment and chairs. Conventional pneumatic cylinders are generally equipped with a fixed air chamber and the operation air pressure is not variable at all, making the working range of such cylinders narrowly limited.